DIRECT-CURRENT MACHINERY 



187 



In Fig. 149 ac shows the relation between the generated e m.f. 

 & and the armature current I. It is called the internal charac- 

 teristic of the generator, be is the drop in generated e.m.f . at full 

 load due to armature reaction. The ordinates of of represent the 

 e.m.f. consumed by the armature resistance. The ordinates of ag 

 are the differences between the corresponding ordinates of ac and of. 



l /4 Load Yi Load 3 4 Load Full Load \\\ Load 



Load Current I 

 I/ I 



FIG. 150. Voltage characteristic of a shunt generator. 



ag therefore shows the relation between the terminal e.m.f. E and 

 the armature current and is called the external voltage character- 

 istic or regulation curve of the generator. 



114. Regulation. The regulation of a generator is defined as 

 the rise in voltage when full load is thrown off expressed ab ?, Der 

 cent of full-load voltage. 



